T E N E T

Transparent Cache Bypass List: Information Page

Revised on 7 January 2005

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Transparent Cache Test

In terms of the GEN2 agreement,  TELKOM operates a large web caching appliance that transparently caches most web requests from most GEN2 sites.  This started under the HEIST agreement in October 2004, and reduces the requirement for shared SAT-3 bandwidth by about 10%.  TENET bore the upfront cost of the cache appliance and bears the monthly service charges from TELKOM.

The default setting is transparent caching of web requests from GEN2 sites.  However, where a site operates one or more site caches, through which all web requests from hosts on the site's network are directed, application may be made to TENET for the transparent caching service to be replaces by a parent caching service to the site's own caches.

Why transparent caching?

Transparent caching, as opposed to parent caching, has the great advantage that it requires no special setting up of users' browsers or cache servers at the sites.  Transparent caching happens automatically. Web requests are routed by the international gateway router to the cache, which delivers the requested page if it is held in cache or otherwise requests it as a proxy on behalf of the original requester (and then retains a copy of the page).

The disadvantage is that there are some web sites, notably those of certain publishers of online journals and databases, that permit or deny access according to the requester's IP address, and would simply deny access to proxy requests bearing the cache's IP address as the source of the request.  Consequently such requests have to be routed directly to the required web site as though there was no cache server.  This necessitates the compilation and maintenance of a "Cache Bypass List" of IP addresses of all such web sites.  This list is incorporated into the gateway's routing tables so as to ensure that requests to the listed IP addresses are not routed to the cache.  

Cache Bypass Address Range List

The efficacy of a Cache Bypass List was demonstrated during the test in March 2004, and the same procedures as were developed then, with valuable assistance from SASLI's Susan Veldsman, are used for maintaining the List.

TENET's Franz Dullaart has built a special interactive Transparent Cache Bypass List web page.  You can use it view the list, query the list to find whether a given URL is covered or not, and submit requests for further URLs (and their IP addresses) to be added to the list.  When you submit a request in this way, the list is immediately updated and the request transmitted automatically by email to the Telkom manager who operates the cache engine.  He (or she) will immediately add the requested URL and its IP address to the bypass list and confirm by email to you and TENET that this has been done.

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